This invention relates to optical waveguide grating devices and, more particularly, to such devices with interleaved sampled and chirped gratings which might be especially useful in WDM networks.
In optical waveguide grating devices, the medium of the waveguide through which light signals are transmitted is periodically or nearly periodically modulated to reflect the light signals at particular wavelengths. Though optical waveguides appear in different forms, such as waveguide-bearing substrates, the fiber Bragg grating has been the recent focus of much development. Hence while the present invention is described in terms of fiber Bragg gratings, it should be understood that much, if not all, of the aspects of the present invention are adaptable to other types of optical waveguide grating devices as well.
Fiber Bragg gratings, and other optical waveguide gratings, are key components in many fiberoptic and telecommunications systems. In fiberoptic telecommunications, gratings can be used for many functions, such as filtering, multiplexing/demultiplexing, and gain equalization in broadband WDM (Wavelength Division Multiplexed) systems where the wavelength of an optical signal is used to direct the signal through a network system to its intended destination. The optical signals of a particular wavelength define a communication channel over the network. In advanced WDM network systems, such as DWDM (Dense WDM) systems, the wavelength spacing for communication channels is much tighter, i.e., narrower, so that more channels can used for a given amount of bandwidth in the network, than in standard WDM networks. DWDM wavelength spacing between channels is set at 0.8 nm (100 GHz) and more recent efforts are directed at channel spacings of 0.4 nm (50 GHz). For the purposes of this application, the terms, "WDM" and "WDM networks," are used broadly to include DWDM and DWDM networks unless stated otherwise.
Gratings are furthermore useful in dispersion compensation, especially for long-distance transmissions. The role of such gratings is expected to expand even more as improvements are made in their design and manufacture.
The present invention provides for such improvements in filtering, multiplexing/demultiplexing, and equalization functions for gratings, and even in compensation for second-order signal dispersion.